Molybdenum Compound Layer Suppresses Catalyst Sublimation
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Solution Overview
Problem
Molybdenum-based composite oxide catalysts used in gas-phase catalytic oxidation reactions suffer from molybdenum sublimation, leading to catalyst deterioration and reduced reaction activity over time, with existing regeneration methods being insufficient for long-term performance maintenance.
Innovation Solution
A catalytic oxidation method involving a molybdenum compound layer with a higher molybdenum sublimation rate than the composite oxide catalyst layer, operated under specific conditions to prevent molybdenum sublimation, including a mixed gas flow of air and water vapor at 440°C, with the molybdenum compound layer having a molybdenum oxide content of 20 mass % or more, and a temperature lower than the catalyst layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a molybdenum-based composite oxide catalyst is used for gas-phase catalytic oxidation reactions, then the catalyst shows high initial activity and effectiveness, but the catalyst deteriorates over time due to molybdenum sublimation, leading to reduced reaction activity and selectivity
Solution Approach 1:
A molybdenum compound layer is introduced above the catalyst layer before the reaction begins. This layer serves as a preliminary protective measure that releases molybdenum compounds during reaction to compensate for sublimation losses from the catalyst, thereby maintaining catalyst activity over extended periods without requiring frequent replacement or regeneration.
2Reliability
If existing regeneration methods (heat treatment at 380-540°C in air) are applied to restore catalyst activity, then some activity recovery is achieved, but the regeneration is incomplete and the catalyst must eventually be replaced
Solution Approach 1:
The molybdenum compound layer acts as a self-replenishing reservoir that continuously supplies molybdenum compounds to the catalyst during reaction. This eliminates the need for external regeneration interventions and enables the catalyst to maintain high activity indefinitely, transforming from a consumable component to a sustainable system.
3Quantity of substance
If the molybdenum compound layer is operated at higher temperature to increase molybdenum release rate, then more molybdenum is supplied to prevent sublimation, but the temperature becomes too high causing unwanted side reactions and reduced selectivity
Solution Approach 1:
The system operates the molybdenum compound layer at a lower temperature (300-400°C) than conventional catalyst operating temperatures, yet still achieves effective molybdenum supply. This parameter optimization balances the release rate with selectivity maintenance, preventing both sublimation losses and unwanted side reactions simultaneously.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively suppresses molybdenum sublimation and maintains catalyst activity, allowing for prolonged operation without significant decreases in performance.
Implementation Method 1
a molybdenum compound layer containing a molybdenum compound and a composite oxide catalyst layer containing a molybdenum composite oxide catalyst are arranged in this order from a reaction raw material supply port side of the tubular reactor, and under a flow of a mixed gas at 440° C. composed of a composition containing 75 vol % of air and 25 vol % of water vapor, a molybdenum sublimation amount (μg/NL) of the molybdenum compound is larger than a molybdenum sublimation amount (μg/NL) of the molybdenum composite oxide catalyst
Implementation Method 2
a molybdenum sublimation amount (μg/NL) of the molybdenum compound is larger than a molybdenum sublimation amount (μg/NL) of the molybdenum composite oxide catalyst
Implementation Method 3
under a flow of a mixed gas at 440° C. composed of a composition containing 75 vol % of air and 25 vol % of water vapor
Data Source
AI summary
An object of the present invention is to suppress performance deterioration of a molybdenum composite oxide-based catalyst at the time of performing gas-phase catalytic partial oxidation with molecular oxygen by using a tubular reactor. The present invention relates to a catalytic oxidation method using a tubular reactor in which a Mo compound layer containing a Mo compound and a composite oxide catalyst layer containing a Mo composite oxide catalyst are arranged in this order from a reaction raw material supply port side and under a flow of a mixed gas containing 75 vol % of air and 25 vol % of water vapor at 440° C., a Mo sublimation amount of the Mo compound is larger than a Mo sublimation amount of the Mo composite oxide catalyst under the same conditions.